1. Field of the Invention
This invention relates to a method of producing high-molecular weight polyphenylene oxide (PPO) by the oxidative coupling of a diortho-substituted phenol in the presence of a catalyst complex of a copper salt and an amine and an activator of morpholinium bromide and alkali.
2. Description of the Prior Art
PPO and methods of producing it are known. Some of these methods are described in Buhler "Spezialplaste" (Akademieverlag Berlin, 1978) and in U.S. Pat. Nos. 3,306,874 and 3,306,875 and in DE-AS No. 22 17 161. However, the methods which involve the oxidative coupling of diortho-substituted phenols in the presence of oxygen by a copper-amine complex have prevailed in industry.
PPO of high molecular-weight can be obtained by the method of DE-OS No. 24 46 425. However, this method is avoided in practice due to the use of very high pressure which involves considerable expense for equipment and safety measures.
DE-OS No. 25-30-827 discloses the use of a catalyst in the preparation of high molecular-weight PPO which contains a copper-amine complex, a metallic bromide, and a quaternary ammonium salt, .sup.+ NR.sub.4 X.sup.-, wherein R is an alkyl, alkenyl or aralkyl radical and X is any anion. The quaternary ammonium salt is, preferably, methyl tri-n-octyl ammonium chloride.
DE-OS No. 22 28 071 describes a method of producing PPO in which phenols are treated with oxygen in the presence of a copper-amine complex and a metal bromide. Further DE-OS No. 22 28 071 discloses that while an accelerating effect is observed for alkali and alkaline earth bromides, such an effect is not observed for non-metallic bromides, such as ammonium bromide.
Japanese Pat. No. Sho-48-32793 discloses a method for producing PPO which uses a catalyst consisting of:
(1) a copper (I) salt, PA1 (2) a compound of an alkali or alkaline earth element which reacts in an alkaline manner, such as lithium carbonate, sodium hydroxide or potassium acetate, and PA1 (3) a nitrile, e.g. propionitrile or phthalodinitrile.
No. Sho-48-32793 teaches the use of this catalyst, instead of a copper-amine complex. Moreover, the oxidation occurs with oxygen or a mixture of oxygen and air in a 1:1 ratio.
None of the methods described heretofore are completely satisfactory in practice. First, oxygen is usually required as an oxidizing agent. In addition to the greater expense which is associated with the use of oxygen, as compared to air, the use of pure oxygen also involves a greater risk to safety.
Secondly, benzene or solvents containing chlorine, such as trichloroethylene, are frequently used in methods currently used to produce PPO. However, due to the suspected carcinogenic nature of these solvents, it would be preferable to avoid their use.
Thirdly, the reaction time for PPO production should be under two hours in order to assure that the reaction procedure is economical. Moreover, if the reaction time is longer than two hours, by-products may easily be formed which add a disturbing discoloration to the reaction mixture.
Finally, a high degree of polymerization is also important. A degree of polymerization of 100 is required for manufacturing threads, fibers, coatings and other products, and a degree of polymerization of 250 is preferred, so that a subsequent molding deformation is completely assured. See DE Pat. No. 20 12 443. This corresponds to a J-value of 50, that is, the relative viscosity change of a 0.5% solution of the reaction product is chloroform at 20.degree. C. in relation to the concentration is over 50 ml/g.
Therefore, a need continues to exist for a process which produces high-molecular weight PPO in a short reaction time, without having to use pure oxygen as an oxidizing agent, and with minimal risk to safety.